Short answers, pulled from the story.
Mercury is the first planet from the Sun and the smallest in the Solar System. It possesses a density that is the second highest in the Solar System at 5.427 grams per cubic centimeter.
Greek thinkers realized Mercury was one and the same object around 350 BC. Before this discovery, astronomers believed the morning star and the evening star were two separate objects.
Mercury's core occupies about 57% of its volume and has an estimated radius of 1,830 kilometers. This core consists of a solid outer layer, a deeper liquid layer, and a solid inner core wrapped in a thin silicate mantle and crust.
Water ice is trapped in the permanently shadowed floors of deep craters at Mercury's poles. Observations by the Goldstone Solar System Radar and the VLA in the early 1990s revealed patches of high radar reflection, and the presence of water ice was confirmed using MESSENGER images of craters at the north pole.
The MESSENGER spacecraft was launched on the 3rd of August 2004 and entered an elliptical orbit around the planet on the 18th of March 2011. It crashed into Mercury's surface on the 30th of April 2015, leaving a crater estimated to be 16 kilometers in diameter.
A single solar day on Mercury lasts exactly two Mercury years or about 176 Earth days. This duration results from the planet's 3:2 spin-orbit resonance where it rotates three times for every two revolutions around the Sun.